1. Field of the Invention
The present invention relates to a continuous pipe producing line, and more particularly, the present invention relates to a rotary looper, which preliminarily stores convolutions of a coil type strip (hereinafter, referred to as xe2x80x9cstripxe2x80x9d) uncoiled by an uncoiler toward a pipe mill, thereby enabling a newly supplied coil of strip to be continuously supplied to the pipe mill.
2. Description of Related Art
Conventionally, in a pipe producing line, a strip is uncoiled by an uncoiler and continuously fed into a pipe mill to produce a completed pipe. Due to the fact that there is an imposed limit, such as a predetermined amount of a strip, that can be continuously fed into the pipe mill, it takes 10 to 20 minutes at best for a unit coil of strip to be fully depleted and a new unit coil of a strip to be supplied into the pipe mill after the depletion. In this roll supply process, an operation of the pipe mill must be interrupted whereby a great deal of effort and time are required.
Therefore, as an alternative for enabling a strip to be continuously fed into a pipe mill without interrupting an operation of the pipe mill, it is regarded as the best method to weld a leading edge of a newly supplied unit coil of strip to a trailing edge of a currently depleted unit coil of strip.
However, since the pipe mill always takes out a strip at a constant rate and the strip has a moving speed corresponding to the take-out rate of the pipe mill, it is impossible, in actual fact, to butt and weld the leading edge of the newly supplied unit coil of strip and the trailing edge of the currently depleted unit coil of strip to each other, while the trailing edge of the currently depleted unit coil of strip is fed into the pipe mill.
To cope with this problem, a vertical type looper is disclosed in the art by Kent Corporation of the United States. In the vertical type looper, the strip is taken out by a separate device where it is to be preliminarily stored on the looper, at the time when a trailing edge of a unit coil of strip is nearly exposed to the outside at a rate which is faster than a normal feed rate of the strip. While the preliminarily stored convolutions of the strip are paid out to a pipe mill to be used in continuous pipe producing, the input of the strip to the looper is stopped for connecting, as by welding, a leading edge of a newly supplied unit coil of strip to the current unit coil of strip. A splicing station is provided between an uncoiler and the looper for making such a connection possible.
Such a conventional vertical type looper is, as shown in FIG. 1, installed on a base member 10 which is arranged between an uncoiler A and a pipe mill B. A pair of input pinch rollers 1 take out a strip 8 which is uncoiled by the uncoiler A, and an input guide 2 guides the strip 8 which is taken out by the pair of input pinch rollers 1. A guide plate 3 is disposed adjacent to a downstream end of the input guide 2. The strip 8, which is taken out by the pair of input pinch rollers 1, passes through the input guide 2 and the guide plate 3. Then, the strip 8 travels inside a plurality of outside basket guide rollers 7, by at least one turn in a state wherein it is brought into close contact with inside surfaces of the outside basket guide rollers 7. Thereupon, the strip 8 forms a U-shaped free loop 8xe2x80x2 as it is turned toward a plurality of inside basket guide rollers 6. The strip 8 also travels outside the plurality of inside basket guide rollers 6 by at least one turn. Thereafter, the strip 8 is transferred around a series of spiral guide rollers 5. After traveling along the series of spiral guide rollers 5, the strip 8 is fed into the pipe mill B while being pulled by a pair of measuring rollers 4.
In this course of transferring the strip 8, by driving the pair of input pinch rollers 1 and thereby taking out the strip 8 into the looper at a speed generally faster than that of the strip 8 out of the looper into the pipe mill B, as the U-shaped free loop 8xe2x80x2 orbits in a traveling direction of the strip 8 around a plurality of outside basket guide rollers 7, outer convolutions and inner convolutions are accumulated or stored on the inside surfaces of the outside basket guide rollers 7 and outside surfaces of the inside basket guide rollers 6, respectively, by the same number. At this time, the strip 8 is brought into close contact with the inside surfaces of the outside basket guide rollers 7 tightly, due to its spring back phenomenon. And as a result of tight frictional contact between the rollers 7 and the strip 8, it is difficult for the strip 8 to further travel around a plurality of outside basket guide rollers 7, when at least one convolution is stored on the inside surfaces of the outside basket guide rollers 7. Consequently, the strip 8 is to be jammed in the input guide 2 or the guide plate 3, or it may be impossible to further take out the strip 8 using the pair of input pinch rollers 1. By reason of this, as the number of outer convolutions of the strip 8 increases, a diameter of a circular space which is defined by the plurality of outside basket guide rollers 7 should also be gradually increased as shown in FIG. 1 by dotted lines, thereby to enable the strip 8 to be stored while being inserted into a gap which is continuously maintained between the outermost convolution and the inside surfaces of the outside basket guide rollers 7. Also, due to the fact that the plurality of outside basket guide rollers 7 are moved outward as described above, as a distance between the innermost outer convolution and the outermost inner convolution varies rather than being constantly kept, the U-shaped free loop 8xe2x80x2 can be bent rather than being flexibly curved. Hence, a diameter of a circular space which is defined by the inside basket guide rollers 6 should also be gradually increased as shown in FIG. 1 by dotted lines, thereby to enable the strip 8 to be tensely stored on the outside surfaces of the inside basket guide rollers 6.
On the other hand, an inside configuration for accomplishing the adjustment of diameters of circular spaces which are defined by the spiral guide rollers 5, the inside basket guide rollers 6 and the outside basket guide rollers 7, respectively, is as complex as the numbers of the spiral guide rollers 5, the inside basket guide rollers 6 and the outside basket guide rollers 7, as schematically shown in FIG. 2, and comprises a multitude of links L, each of which is driven by a hydraulic system or a pneumatic system. Thus, because fabricating and assembling procedures of a variety of components constituting the looper are greatly complicated and difficult to implement, fabricating cost is increased, a failure rate is elevated and noise is generated.
If an initial width between the innermost outer convolution and the outermost inner convolution is set large, such that the strip 8 has a small thickness, as an arc which is defined by the U-shaped free loop 8xe2x80x2 as increased in its length, the strip 8 is likely to be bent rather than smoothly orbiting around the inside basket guide rollers 6 and the outside basket guide rollers 7. Therefore, in the case of the strip 8 having a small thickness, cumbersomeness is caused by the fact that initial positions of the plurality of outside basket guide rollers 7 must be adjusted thereby to shorten the initial width between the innermost outer convolution and the outermost inner convolution.
Moreover, because the strip 8 which is taken out by the pair of input pinch rollers 1 must be always transferred to the looper in a direction which is tangential to an upper end surface of the lowermost outside basket guide roller 7, the pair of input pinch rollers 1, the input guide 2 and the guide plate 3 are structured in a manner such that they can be simultaneously lowered by the link arrangements as the plurality of outside basket guide rollers 7 are moved outward, whereby complexity of the entire looper is augmented, fabricating cost is increased and failure frequently occurs.
In addition, while the looper is operated, the convolutions of the strip 8 always travel around a circular path in a state wherein they are brought into close contact one with another, frictional force is generated between two adjoining convolutions of the strip 8 due to elasticity of the strip 8. Accordingly, power which is derived by the pair of input pinch rollers 1, must be fairly large to enable the strip 8 to travel around the outside basket guide rollers 7 and the inside basket guide rollers 6, and thereby, frictional noise and dust generation by the strip 8 are increased.
In the meanwhile, in the conventional vertical type looper constructed as mentioned above, since an output position of the strip 8 where it is outputted to the pipe mill B is deviated by a distance of W from an input position of the strip 8 where it is inputted to the looper, in the case that the vertical type looper is installed at a superannuated factory which uses another strip accumulator or strip storing device such as a hoop cage or the like, an installation must be executed in a manner such that a center of the output position of the strip 8 is first aligned with a center of the pipe mill B and then, a center of the uncoiler A is moved from the center of the output position of the strip 8 by the deviation amount of W.
Specifically, the conventional vertical type looper encounters a problem from the standpoint of its construction in that at least one convolution should always be accumulated on the outside basket guide rollers 7 or the inside basket guide rollers 6. If at least one convolution is not accumulated on the basket guide rollers 7 or 6 while the pipe mill B is being continuously operated, it causes serious problems with the operation.
Consequently, in the vertical type looper, if the number of convolutions is no greater than 2, the strip 8 on the basket guide rollers 7 and/or 6 needs to be accumulated sufficiently. The strip accumulating operation must be repeatedly performed whenever the number of the convolutions is decreased to a number no greater than 2, as the convolutions are paid out into the pipe mill B. Then, it may be impossible to secure enough time to weld a leading edge of a newly supplied unit coil of strip 8 to a trailing edge of a current unit coil of strip 8, if a coiled amount of the strip 8 is small and a sufficient amount of the strip 8 cannot be accumulated on the rollers 7 and/or 6. Thereby, it is impossible to keep the continuous operation of the pipe mill B.
Hence, a higher grade of skillfulness is required and an operator should pay close attention to the operation of the vertical type looper, since a size of the strip must be precisely managed with the conventional vertical type looper. Furthermore, the conventional vertical type looper is proved costly to be used in a small-scale pipe producing line and it is difficult to secure a skilled operator. So, the vertical type looper is mainly used in a large-scale pipe producing line presently.
The present invention has been made in an effort to solve the problems occurring in the related art. The object of the present invention is to provide a rotary looper which allows convolutions of a strip to be preliminarily stored by a rotary drum and a lead drum while not being damaged at all. This invention, therefore, minimizes a defective fraction, simplifies respective operating arrangements, and thereby outstandingly reduces manufacturing cost and failure rate. Furthermore, it enables an entering position of the strip and a discharging position of the strip to be aligned with each other on a straight line, thereby to be capable of being suited to an existing pipe producing line as it is.
In order to achieve the above object, according to the present invention, there is provided a rotary looper comprising: a base member; a fixed drum installed on the base member and having a plurality of spiral guide rollers; a pair of pinch rollers and a series of lead rollers sequentially disposed at an inputting side of the base member; a pair of measuring rollers disposed at a discharging side of the base member; a plurality of inside basket rollers circularly installed along a circumferential outer surface of the fixed drum; a rotary drum disposed around the fixed drum in a manner such that the rotary drum is rotatably driven by a motor via a rail which is wound around a plurality of rail rollers which are circularly installed on the base member; a lead drum rotatably disposed in a portion of the rotary drum; a plurality of inside basket guide rollers circularly installed along a circumferential inner surface of the rotary drum; a plurality of outside basket rollers circularly installed along a circumferential outer surface of the rotary drum; and a plurality of outside basket guide rollers circularly installed on the base member outward of the plurality of outside basket rollers in a manner such that they are spaced apart from the plurality of outside basket rollers by a predetermined distance.